As compared with widely used amorphous silicon (a-Si), an amorphous (noncrystalline) oxide semiconductor has high carrier mobility, a high optical band gap, and film formability at low temperatures, and therefore, has been highly expected to be applied for next generation displays which are required to have a large size, high resolution, and high-speed drive, resin substrates which has low heat resistance, and the like.
In the oxide semiconductors, amorphous oxides containing indium, gallium, zinc, and oxygen (In—Ga—Zn—O, which may hereinafter be referred to as “IGZO”), and amorphous oxides containing indium, zinc, tin, and oxygen (In—Zn—Sn—O, which may hereinafter be referred to as “IZTO”), are preferably used because of their having very high carried mobility. For example, Non-Patent Documents 1 and 2 disclose a thin-film transistor (TFT) including an IGZO semiconductor thin film of In:Ga:Zn=1.1:1.1:0.9 (atomic % ratio) as a semiconductor layer (active layer) of the thin-film transistor (TFT).
As examples of using an IZTO semiconductor, there can be mentioned, for example, Patent Documents 1 and 2, as well as Non-Patent Documents 3 and 4. Patent Document 1 discloses an amorphous oxide (IZTO) containing elements, such as In, Zn, and Sn, and Mo, where Mo has an atomic composition ratio of 0.1 to 5 atomic % with respect to the total number of metal atoms in the amorphous oxide. A TFT including an active layer of IZTO doped with Mo is disclosed in the examples of Patent Document 1.